As shown in FIG. 1, an Evolved Packet System (EPS) consists of an access network and an Evolved Packet Core (EPC) network, wherein the access network can be an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and the like; the EPC comprises a Mobility Management Entity (MME), a Serving Gateway (S-GW), a Packet Data Network Gateway (P-GW), a Home Subscriber Server (HSS), a 3GPP Authentication Authorization Accounting server (3GPP AAA server), a Policy and Charging Rules Function (PCRF) and other support nodes.
In which, the MME is responsible for the control plane related work including mobility management, non-access layer signaling process and user context management and so on; the S-GW is an access gateway equipment connected with the E-UTRAN, which is responsible for forwarding data between the E-UTRAN and the P-GW and caching the paging waiting data; the P-GW is a boundary gateway of 3GPP evolved packet system and Packet Data Network (PDN), which is responsible for performing the access of user terminal to PDN and forwarding data between the EPS and the PDN and so on; the PCRF is a policy and charging rule function entity which is connected with an operator Internet Protocol (IP) service network via a receiving interface Rx to obtain service information; and furthermore, the PCRF is connected with the gateway equipments in network via Gx/Gxa/Gxc interfaces, which is responsible for initializing an IP bearer establishment to guarantee the Quality of Service (QoS) of the service data and perform the charging control.
The EPS also supports the accesses of UE by the other non-3GPP systems besides the E-UTRAN, wherein the access of non-3GPP system is realized via an S2a/b/c interface and the P-GW is used as a data anchor point of the access of 3GPP system and the access of non-3GPP system. In the system architecture of EPS, non-3GPP system includes a trusted non-3GPP IP access network and an untrusted non-3GPP IP access network, in which, the trusted non-3GPP IP access network can be connected with P-GW directly via an S2a interface, and the untrusted non-3GPP IP access network can be connected with P-GW via an evolved packet data gateway (ePDG), wherein the interface between the ePDG and the P-GW is S2b. S2c is an interface between an User Equipment (UE) and the P-GW, applying the mobile IPv6 support for Dual Stack Hosts and Routers (DSMIPv6) protocol to provide control and mobility management.
At present, multiple access becomes one of the research subjects of the EPS. Multiple access means that EPC supports the simultaneous access of UE, through multiple access networks, to one or more PDNs via the same P-GW or different P-GWs. As shown in FIG. 2, UE is under the coverage of the non-3GPP access network and the 3GPP access network simultaneously, and accesses through the non-3GPP IP access network and the 3GPP access network, to the same PDN via the same P-GW. In this case, the UE attaches to the EPC through a plurality of access networks; P-GW allocates an IP address for UE; and a PDN connection exists between UE and PDN. Since different services require different network transmissions, a proper access network can be selected to transmit services according to the characteristics of the services with the multiple access technology, moreover a plurality of access networks can share network load, thereby network congestion is avoided. For example, when the non-3GPP access network is WiFi, the service data flow of Http and Ftp can be sent to UE through the WiFi access network and the service data flow of VoIP can be sent to UE through the 3GPP.
With the multiple access mothed and the multiple access system of EPS based on the related art, in the condition that the selected P-GW does not support a multiple access when UE performs an initial attachment, the P-GW cannot identify the multiple access request initialized by the UE, which does not know whether or not the P-GW supports the multiple access and defaults that the P-GW supports the multiple access. Therefore the UE still initializes a multiple access request, which resulting in a waste of network resource and a poor experience of users. For above problems existing in the prior art, no effective solution has been provided by far.